Reference may be made to one or more of the following patent documents: European patent application 87 89 0020.8 filed Jan. 30, 1987 and published as 0 231 164A2 on Aug. 5, 1987 citing as inventors Dr. Hans Loeschner, Dr. Gerhard Stengl and Dr. Peter Wolf; U.S. Pat. No. 4,823,011 issued Apr. 18, 1989 to Gerhard Stengl and Hans Loeschner; U.S. Pat. No. 4,985,634 issued Jan. 15 1991 to Gerhard Stengl and Hilton F. Glavish, all commonly owned with the present application, and to the references and documents cited therein. Reference may also be made to U.S. Pat. Nos. 4,563,587 (Ward et al), 4,740,694 (Nishimura et al) and 4,755,685 (Kawanami et al).
As will be apparent from these documents among others, the production of semiconductor components can be effected by lithography utilizing a series of steps, in one of which, a structure of a mask may be imaged upon a wafer.
In a simplified version, the lithographic process for producing semiconductor components begins with the application of a thin layer of a light-sensitive material, referred to generally as a photoresist or simply as a resist, upon a wafer forming the semiconductor substrate, generally a silicon wafer.
A lithographic apparatus projects a structure of a mask upon the resist coating of the wafer and usually the extent of the projected structure on the wafer is much smaller than the area of the wafer. Subsequently, the wafer is shifted and the structure of the mask is then projected on another location of the wafer.
These steps of projection and shifting are repeated until the entire wafer surface is used.
The resist is then developed and the wafer has a desired pattern in the form of a multiplicity of resist-free locations or zones. In subsequent steps, the wafer can be subjected to processes such as etching, ion implantation or application and diffusion of doping materials to form the desired local compositions and structures.
After these further steps, the wafer is inspected, coated again with a resist, and subjected once more to the lithographic steps so that after 8 to 15 repetitions of these steps, a checkerboard arrangement of substantially identical microcircuits are formed on the wafer. The wafer can then be cut up, the microcircuits encapsulated and provided with terminals, etc.
Most of the present-day projection lithographic processes utilize light to irradiate the resist. However, the need for ever smaller structures and higher densities of the components of the microcircuits has resulted in intensive research into other irradiation methods which are not limited in their resolution to that of light with relatively large wavelengths. For example, the use of X-rays has been attempted and also other processes like ion-beam lithography, although these methods have not found as widespread an application as the light-beam photolithographic processes.